The invention relates to an electrical disconnector comprising a first contact which is mounted to move in an axial direction relative to a fixed second contact and which co-operates therewith to establish an electrical connection, and a rod which extends along the axial direction and which is driven to move the first contact relative to the second contact.
The invention applies more particularly to a high voltage electrical disconnector having a metal case in which the moving and fixed contacts are located, the case being filled with a dielectric gas such as SF6. The rod for driving the moving contact passes through the metal case in a sealed manner and it is usually displaced in translation by a mechanical control means.
Patent application EP 0 348 645 discloses a disconnector having two moving contacts formed by two coaxial cylinders and displaced so as to be connected successively to a fixed arcing contact and to a fixed permanent contact (for passing the permanent current). The control mechanism for controlling the moving contacts uses two aligned helical springs that are separated by a collar fixed to a drive rod which is in axial alignment with said springs. The disconnector arrangement disclosed enables the moving contacts to have a travel speed that is much faster than that of the drive rod during the operations of opening or closing the electrical connection.
In general, when the disconnector is operated on capacitive current (of low amperage under very high voltage), electric arcs are created between the moving contact and the fixed contact and generate very high frequency line transients (of MHz order) which are harmful to the connected equipment. The faster the disconnector, the smaller the number of arcs struck. To this end, the above-mentioned patent application uses a moving arcing contact that is moved at high speed to connect or disconnect a fixed arcing contact which can also be called a xe2x80x9ctransient-current contactxe2x80x9d. Just after said arcing currents have been connected, the permanent contacts can be moved towards each other and connected together without striking an electric arc.
However, the two-stage connection provided by the two moving contacts in such a device does not deal with certain problems:
Firstly, despite the reduction in the number of arcs struck as a result of the increased switching speed, each high voltage front nevertheless remains harmful to the connected equipment. In order to reduce the steepness and the height of said fronts, it is,known to use resistors connected to the fixed arcing contact. If the current produced by the arcs being struck passes in full via said resistors, the fronts are damped considerably.
As a result of the disposition of its fixed contacts, the above-mentioned device does not enable electric arcs to be struck only on the fixed arcing contact. The insulating distance between the moving arcing contact and the fixed permanent contact can become insufficient if the voltage exceeds a certain threshold, in which case arcs may be struck between the contacts, resulting in harmful voltage surges since the voltage is not attenuated by any resistors.
In addition, such a device having two moving contacts implies that a transient current will flow while waiting for the permanent contacts to be connected. As a result of the limited section of the moving arcing contact, the transient current must remain beneath a critical threshold, beyond which the amount of heat produced would be harmful to the arcing contacts, particularly since this current lasts for a long time. This problem occurs specifically when switching the disconnector on busbar transfer current, which can be as great as thousands of amps.
In order to remedy the drawbacks of the prior art, the invention provides an electrical disconnector comprising a first contact which is mounted to move along an axial direction relative to a fixed second contact and which co-operates therewith to establish an electrical connection, and a rod which extends along said axial direction and which is driven to move the moving contact relative to the fixed contact, wherein the moving contact is a hollow tube having a first end which faces the fixed contact and a second end opposite to the first end, wherein the disconnector comprises a piston slidable inside the moving contact, the piston being mounted on the rod and having a first end facing towards the fixed contact and a second end opposite from the first end, wherein a first spring is interposed between the first end of the moving contact and the first end of the piston, wherein a second spring is interposed between the second end of the moving contact and the second end of the piston, wherein a first locking system is provided to lock the moving contact in the axial direction during a closure operation at the same time as the first spring is compressed between the piston and the first end of the moving contact, said first locking system retracting after the first spring has been compressed by a certain amount so that the moving contact is connected to the fixed contact under the effect of the first spring relaxing, and wherein a second locking system is provided to prevent the moving contact from moving in the axial direction during an opening operation while the second spring is being compressed between the piston and the second end of the moving contact, said second locking system retracting after the second spring has been compressed by a certain amount so that the moving contact is disconnected from the fixed contact under the effect of the second spring relaxing.
The device enables high voltages to be switched at high speed while enabling high currents to be passed.